Conventionally, a coupling structure between a front pillar and a side sill of an automobile has been formed by coupling the lower end portion of the front pillar, which is extended in the up-down direction of the automobile and formed into a shape having a closed cross-section by fitting together a front pillar outer and a front pillar inner, to the front end portion of the side sill, which is extended in the front-rear direction of the automobile and likewise formed into a shape having a closed cross-section.
Aside from this, in recent efforts to further reduce the weight of automobiles, particularly, the front pillar outer is made from steel sheet, which is a material with a high strength.
However, in order to enable the lower end portion of the front pillar to be coupled to the side sill, the front pillar is formed into a bent structure, which is largely bent out from the up-down direction of the automobile toward the rear side of the automobile by drawing a long curve.
Therefore, use of high-strength steel sheet as the material of the front pillar outer makes it difficult to mold the front pillar outer into a predetermined shape by one pressing, which leads to a drop of the productivity.
Hence, conventionally, in order to make the structure of the front pillar as simple as possible to improve the productivity, simplification of the structure has been attempted by forming the front pillar into a three-piece structure, which includes from the top of the automobile downward, an upper portion, a center portion joined to the lower end of the upper portion, and a lower portion joined to the lower end of the center portion, which are joined together at their ends, while at the same time, efforts have been made to form the lower end structure of the lower portion into as short a shape as possible (see Patent Document 1 and Patent Document 2).
Patent Document 1: Japanese Patent Application Publication No. 2008-222039
Patent Document 2: Japanese Patent Application Publication No. 2009-61991